1. Field of the Invention
This invention relates generally to the field of loudspeakers. More particularly, the invention relates to the imparting of sound-damping properties to one or more structures or components of a loudspeaker.
2. Related Art
An audio loudspeaker system typically includes a driver unit that serves as an electroacoustic transducer. Electrical signals encoding auditory information are fed to the driver unit, and the driver unit converts the electrical signals to acoustic signals. The acoustic signals propagate through a suitable fluid medium, such as air, in the manner of waves. The pressure differences in the medium characterized by these waves are interpreted by a listener as sound. The quality of the auditory signal produced from a driver unit can be improved or enhanced by coupling the driver unit to an appropriate sound-directing structure that encloses a volume of medium to which sound waves are first received from the driver unit. A horn is one example of a sound-directing structure. Typically, a horn includes one open end coupled to the driver unit and another open end or mouth downstream from the driver-side end from which sound waves disperse to a listening area. The mouth may be formed as part of a waveguide connected to the horn, or the sound-directing structure may be characterized as being either a horn or a waveguide. The horn often has a flared design such that the interior defined by the horn expands or increases from the driver-side end to the mouth. The structure of the horn (or waveguide) and thus its interior can be shaped so as to guide the sound waves according to desired criteria, such as concentrating and/or directing the sound waves.
In the design and manufacture of audio loudspeakers, horns, waveguides, or other enclosures or structural features typically include regions that constitute flat or curved panels, and that are desired for imparting stiffness or rigidity for mechanical and/or acoustic purposes. In addition to providing structural characteristics, it may be desirable for these regions to also provide acoustic damping properties for sound absorption, deadening, and isolation, particularly between opposing inside and outside surfaces of such panel-like structures. As an example, in the throat portion of the horn of a loudspeaker, the internal surface is exposed to a field of high-energy sound pressure produced by the driver. At the exterior surface opposite to the internal surface, sound vibrations are unwanted due to their potential influence on the directivity and overall acoustic performance of the loudspeaker. This problem can stem from one or more resonance effects within the audio frequency range as determined by physical considerations such as mass and compliance. Accordingly, for many implementations it would be desirable that an isolating or dampening means be employed to ameliorate any adverse effect of such sound vibrations at the exterior side of the throat portion of a horn or other sections of a sound-directing component of a loudspeaker.
One approach to addressing this problem is to make certain parts of the loudspeaker thicker and thus more massive and rigid. This approach, however, is often undesirable because it results in an unacceptable increase in weight, cost and size.
An alternative approach may be strategically deploying damping material at one or more parts of the loudspeaker to suppress resonant effects by lowering the Q of the mechanical resonance, thereby causing a portion of the unwanted acoustic energy to be dissipated by conversion into heat energy, rather than transmitted to the interior and exterior surfaces. A coating of adherent, flexible, elastic or visco-elastic material may be formulated and applied to exterior surfaces of a loudspeaker to provide the required balance of stiffness, mass and damping. For many implementations, and particularly commercial implementations, this approach is considered to be unacceptable due to reliability problems as well as aesthetic and marketing disadvantages.
Therefore, there is a need for providing loudspeakers or loudspeaker components with sound-damping properties that overcome the disadvantages set forth above and others previously experienced. For loudspeakers or loudspeaker components requiring one or more flat and/or curved panel-like regions that have hard surfaces to impart stiffness to the loudspeaker, there is a need for providing such regions with the ability to attenuate through-panel sound transmission and suppress resonances. There is also a need for providing a sound-damping structure for a loudspeaker that exhibits a balance of stiffness, mass and damping, along with the ability to selectively address potential resonant frequencies in certain structural configurations. There is also a need for providing a sound-damping structure for a loudspeaker that can be economically manufactured in a simple process using commercially available materials.